The emitter current of a transistor is 1 mA. If 1% of the emitted current carriers are lost in the base recombination, what is the value β? Identify from the given options.

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ALP CBT 2 Electronic Mechanic Previous Paper: Held on 21 Jan 2019 Shift 1

Answer 1

Concept:

For a transistor, the base current, the emitter current, and the collector current are related as:

I_E = I_B + I_C

where I_C = β_dc I_B

β_dc = Current gain of the transistor which is defined as:

\(β=\frac{I_C}{I_B}\)

β is the fraction of emitter current passing to the collector side.

Calculation:

Let the emitter current be I_E.

Since 1% of the emitted current carriers are lost in the base recombination, the collector current will be 99% of the emitter current, i.e.

I_C = 0.99 I_E

And the base current will be 1%, i.e. 0.01 I_E

∴ β will be:

\(β=\frac{I_C}{I_B}=\frac{0.99I_E}{0.01I_E}\)

β = 99

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